To understand the molecular genetics of obesity in humans. There is clear evidence based on twin, adoption and segregation studies, of a substantial genetic basis for susceptibility to obesity. The specific genes, however, remain unknown. This project examines the role of human homologs of genes which produce obesity in rodents, as well as other candidate genes, by use of linkage mapping, mutation analysis and direct measurement of the protein products of these genes. Over 15,000 affected individuals (children and adults) and family members are being recruited and studied.